1. Field of the Invention
The present invention relates to an interface for transferring workpieces such as semiconductor wafers, reticles and flat panel displays between a carrier for the workpieces and a process tool, and in particular to a system facilitating quick and easy mounting of a load port onto a BOLTS interface.
2. Description of Related Art
A SMIF system proposed by the Hewlett-Packard Company is disclosed in U.S. Pat. Nos. 4,532,970 and 4,534,389. The purpose of a SMIF system is to reduce particle fluxes onto semiconductor wafers during storage and transport of the wafers through the semiconductor fabrication process. This purpose is accomplished, in part, by mechanically ensuring that during storage and transport, the gaseous media (such as air or nitrogen) surrounding the wafers is essentially stationary relative to the wafers, and by ensuring that particles from the ambient environment do not enter the immediate wafer environment.
A SMIF system has three main components: (1) minimum volume, sealed pods used for storing and transporting wafers and/or wafer cassettes; (2) an input/output (I/O) minienvironment located on a semiconductor processing tool to provide a miniature clean space (upon being filled with clean air) in which exposed wafers and/or wafer cassettes may be transferred to and from the interior of the processing tool; and (3) an interface for transferring the wafers and/or wafer cassettes between the SMIF pods and the SMIF minienvironment without exposure of the wafers or cassettes to particulates. Further details of one proposed SMIF system are described in the paper entitled "SMIF: A TECHNOLOGY FOR WAFER CASSETTE TRANSFER IN VLSI MANUFACTURING," by Mihir Parikh and Ulrich Kaempf, Solid State Technology, July 1984, pp. 111-115.
SMIF pods are in general comprised of a pod door which mates with a pod shell to provide a sealed environment in which wafers may be stored and transferred. At present, there are different configurations of SMIF pods owing in part to the different wafer sizes and tool interface orientations currently found in wafer fabs. In addition to existing 200 mm wafers, processing of 300 mm wafers has been introduced in recent years. Different pods and pod handling equipment are employed depending on whether processing is being performed on 200 mm or 300 mm wafers. Additionally, SMIF pods may either be bottom opening or front opening. In bottom opening SMIF pods, the pod door is provided horizontally at the bottom of the pod, and the wafers are supported in a cassette which is in turn supported on the pod door. In front opening pods, the pod door is located in a vertical plane, and the wafers are supported in parallel horizontal planes on shelves mounted within the pod shell. Such pods are commonly referred to as front opening unified pods, or FOUPs.
Process tools typically include load ports affixed to their front end so that pods or stand-alone cassettes may be positioned adjacent the process tool in preparation for the wafers and/or wafer cassettes to be transferred into the process tool. For wafer fabs utilizing 300 mm wafers in front opening pods, a vertically oriented frame, commonly referred to as a box opener-loader tool standard interface (or "BOLTS" interface), has been developed by Semiconductor Equipment and Materials International ("SEMI"). The BOLTS interface attaches to, or is formed as part of, the front end of a process tool, and provides standard mounting points for a load port to attach to the process tool. The BOLTS interface also provides a reference position so that a fixed distance between the BOLTS interface and the center of a wafer on the load port may be defined. Thus, although equipment manufactures make various configurations of load ports for 300 mm front opening pods, each load port may be operationally connected to a process tool as long as the load port is configured to attach to the defined standardized BOLTS interface frame.
Presently, connection of a tool load port to a BOLTS interface is a cumbersome and difficult task. Tool load ports for 300 mm wafers are generally large and heavy. Although their configuration may vary significantly, a typical load port may have a height and width of four to five feet, by eighteen inches, and a weight of approximately sixty pounds. In order to bolt a tool load port onto a BOLTS interface, it is presently necessary to cart the load port to the interface, position the load port at the proper location on the BOLTS interface, and thereafter bolt the load port to the interface. Additionally, when attaching the load port to the BOLTS interface, several small adjustments are necessary to properly position the load port on the interface. Two people are required to lift and properly align the load port to the BOLTS interface plate, and a third is required to screw the load port to the BOLTS interface plate once properly positioned. This process is both time and man-hour consuming, and may create physical strains or injuries to the installing technicians.